Self-aligned floating gate in a vertical memory structure

ABSTRACT

A memory device or electronic system may include a memory cell body extending from a substrate, a self-aligned floating gate separated from the memory cell body by a tunneling dielectric film, and a control gate separated from the self-aligned floating gate by a blocking dielectric film. The floating gate is flanked by the memory cell body and the control gate to form a memory cell, and the self-aligned floating gate is at least as thick as the control gate. Methods for building such a memory device are also disclosed.

BACKGROUND

1. Technical Field

The present subject matter relates to semiconductor memories, and morespecifically, to three-dimensional floating-gate flash memory.

2. Discussion

Many types of semiconductor memory are known. Some memory is volatileand will lose its contents if power is removed. Some memory isnon-volatile and will hold the information stored in the memory evenafter power has been removed. One type of non-volatile memory is flashmemory which stores charge in a charge storage region of a memory cell.In a floating gate flash cell, a conductive floating gate, positionedbetween the control gate and the channel of a metal-oxide silicon fieldeffect transistor (MOSFET), is used to store a charge. In a charge trapflash (CTF) cell, a layer of non-conductive material, such as a nitridefilm, is used to store charge between the control gate and the channelof a MOSFET. The threshold voltage of the MOSFET-based flash cell can bechanged by changing the amount of charge stored in the charge storageregion of the cell, and the threshold voltage can be used to indicate avalue that is stored in the flash cell.

One architecture in common use for flash memories is a NAND flasharchitecture. In a NAND flash architecture, two or more flash cells arecoupled together, source to drain, into a string, with the individualcell control gates coupled to control lines, such as word lines. Selectgates, which may be standard MOSFETs, may be coupled to the NAND stringat either end, to couple the NAND string to a source line at one end ofthe NAND string, and to a bit line at the other end of the NAND string.

Some NAND flash devices may create stacks of flash memory cells in athree-dimensional array NAND strings. A stack of flash cells may includeany number of flash cells with the source, channel, and drain arrangedvertically so that as the cells are positioned, one on top of the other,they form a vertical NAND string. The individual memory cells of thevertical NAND string may be on different layers arranged around a bodythat extends outward from the substrate, with the charge storage regionlocated on the same plane as the control gate, extending outwardhorizontally from the body.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute partof the specification, illustrate various embodiments. Together with thegeneral description, the drawings serve to explain various principles.In the drawings:

FIGS. 1A and 1B respectively show side and top cross-sectional views ofan embodiment of a memory cell with a self-aligned floating gate;

FIG. 1C shows a top cross-sectional views of an alternative embodimentof a memory cell with a self-aligned floating gate;

FIG. 2A shows a side cross-section of an embodiment of a vertical NANDflash string with self-aligned floating gates;

FIG. 2B shows a schematic of the NAND flash string of FIG. 2A;

FIG. 3 is a block diagram of an embodiment of an electronic system usingthree dimensional flash memory with self-aligned floating gates;

FIG. 4 is a flowchart of an embodiment of a method to fabricate a threedimensional memory structure with self-aligned floating gates; and

FIG. 5A-L show cross-sectional side views of various stages of themethod shown in FIG. 4.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant teachings. However, it should be apparent to those skilledin the art that the present teachings may be practiced without suchdetails. In other instances, well known methods, procedures andcomponents have been described at a relatively high-level, withoutdetail, in order to avoid unnecessarily obscuring aspects of the presentconcepts. A number of descriptive terms and phrases are used indescribing the various embodiments of this disclosure. These descriptiveterms and phrases are used to convey a generally agreed upon meaning tothose skilled in the art unless a different definition is given in thisspecification. Reference now is made in detail to the examplesillustrated in the accompanying drawings and discussed below.

FIGS. 1A and 1B respectively show side and top cross-sectional views ofan embodiment of a memory cell 100 with a self-aligned floating gate.Cross-section line B:B is shown in FIG. 1A to show the location of thecross-sectional view of FIG. 1B, and cross-section line A:A is shown inFIG. 1B to show the location of the cross-sectional view of FIG. 1A. Thememory cell 100 shown in FIGS. 1A and 1B may be a part of a largervertical memory structure extending out from a substrate. The memorycell 100 may be formed around a memory cell body 110 that may be madefrom a semiconductor material, which may be a polysilicon material insome embodiments, although other embodiments may use other materialssuch as doped crystalline silicon, gallium arsenide, germanium, or othersemiconductors. The memory cell body 110 may extend out from thesubstrate. The substrate may include a base wafer or other structureupon which various materials be deposited, grown, or otherwise put inplace in various patterns, layers, and thicknesses with a variety ofprocesses to create the circuitry for the memory. The substrate mayinclude some number of layers of other materials on the wafer below thememory cell body 110. The memory cell body 110 may have a pillar-likeshape with a substantially circular cross-section in some embodiments,and the memory cell body 110 may be shared between several memory cells,with an individual memory cell 100 using a portion of the pillar for itschannel.

In accordance with one or more embodiments, the substrate may be thoughtof as being a horizontal surface with the memory cell body extending upfrom the substrate in a generally vertical direction. The various layersdescribed herein may have a generally horizontal orientation with athickness measured in a vertical direction. A film may have anyorientation and may conform to a surface having any geometry. A film mayhave a thickness that is measured in a perpendicular direction from thelocal surface that the film is deposited on. The word surround and itsconjugations in this disclosure and claims may be interpreted assurrounding on a horizontal plane. In other words, a first feature maybe said to surround a second feature if the first feature completelysurrounds the second feature in at least one horizontal (or top view)cross-section, even if there are other cross-sectional views, horizontalor some other orientation, where the first feature may not fullysurround the second feature.

The memory cell 100 may be interposed between a first tier insulatinglayer 130 and a second tier insulating layer 136. The tier insulatinglayers 130, 136 may be made from any non-conductive material, but may bemade from silicon oxide in at least one embodiment. Some embodiments mayuse another oxide or a nitride for the tier insulating layers 130, 136.A floating gate 120 is separated from the memory cell body 110 by atunneling dielectric film 122 and a control gate 124 is separated fromthe floating gate 120 by a blocking dielectric film 126. In theembodiment shown, the floating gate 120 is separated from the tierinsulating layers 138, 136 by the blocking dielectric film 126. Thefloating gate 120 is flanked by the memory cell body 110 and the controlgate 124 to form a memory cell. The thickness 140 of the floating gate120 is at least as thick as the thickness 144 of the control gate 124.In the embodiment shown in FIG. 1A, the thickness 140 of the floatinggate 120 is approximately the same as the thickness 144 of the controlgate 124. This may be accomplished by having the thickness of thesacrificial layers 132, 134 be approximately the same as the thicknessof the blocking dielectric film 126 and leaving the blocking dielectricfilm 126 in place on the tier insulating layers 130, 136 as the floatinggate 120 is formed.

In some embodiments, the control gate 124 is sandwiched by sacrificiallayers 132, 134. The sacrificial layers 132, 134 may be made from aninsulating material that may be the same material, or may be a differentmaterial, than the tier insulating layers 130, 136. Whatever material isused for the sacrificial layers 132, 134, it is differentiated from thematerial of the tier insulating layers 130, 136, meaning that there is adifference in the materials so that the material of the sacrificiallayers 132, 134 may be etched at a faster rate than the material of thetier insulating layers 130, 136. The other various parts of the memorycell 100 may be made from a variety of materials, depending on theembodiment, but in some embodiments, the memory cell body 110, thefloating gate 120 and the control gate 124 are made, at least in part,of polysilicon, the tunneling dielectric film 122 is made with an oxide,such as silicon oxide, and the blocking dielectric film 126 is aninter-poly dielectric made from a nitride film, or other high dielectricfilm, sandwiched between two oxide films. In some embodiments, theblocking dielectric film 126 is made with a film of silicon nitride,aluminum oxide, hafnium oxide, or hafnium silicate sandwiched betweentwo films of silicon oxide.

In the embodiment shown in FIGS. 1A and 1B, the floating gate 120 mayform an annulus around the memory cell body 110, and that the controlgate 124 surrounds the floating gate 120. In other embodiments, thecontrol gate 124 may not fully surround the memory cell body 110 withthe floating gate which may allow for two or more separate memory cellsto be formed in the same layer around the memory cell body 110. In suchcases, or in certain other embodiments, the control gate may not fullysurround the floating gate.

With the geometry shown for the memory cell 100, the shortest path fromany point in the control gate 124 to the memory cell body 110 passesthrough the floating gate 120, as shown by the arrow 150. To avoidpassing through the floating gate 120, as shown by arrow 152, the pathis at an angle, which is not the shortest distance from the control gate124 to the memory cell body 110. In such a geometry, the control gate124 and the floating gate 120 are self-aligned, which may reducetunneling current between the control gate 124 and the channel of thememory cell in the memory cell body 110, eliminate an electron trappinglayer along the sidewall of the floating gate 120 in a direct electricfield line from the control gate 124 to the memory body 110, and mayincrease the reliability of the floating gate flash memory cell 100.

FIG. 1C shows a top cross-sectional view of an alternative embodiment ofa memory cell 160 with a self-aligned floating gate. The memory cell 160shown in FIG. 1C may be a part of a larger vertical memory structureextending out from a substrate and is similar to the memory cell 100shown in FIGS. 1A and 1B. The memory cell 160 may be formed around amemory cell body 161 that may be made from a semiconductor material, andthe memory cell body 110 may be shared between several memory cells,with an individual memory cell 100 using a portion of the pillar for itschannel. The memory cell 160 may be interposed between a first tierinsulating layer 171 and a second tier insulating layer 172. A floatinggate 163 is separated from the memory cell body 161 by a tunnelingdielectric film 162 and a control gate 165 is separated from thefloating gate 163 by a blocking dielectric film 164. The floating gate163 is flanked by the memory cell body 161 and the control gate 165 toform a memory cell. The control gate 165 is sandwiched by sacrificiallayers 173, 174.

In the embodiment shown, the blocking dielectric film 164 is notinterposed between the floating gate 163 and the tier insulating layers171, 172. This may be accomplished during fabrication by not forming theblocking dielectric film 164 in those locations, or by removing it afterit is formed, depending on the embodiment. The thickness 180 of thefloating gate 163 is at least as thick as the thickness 181 of thecontrol gate 165. In the geometry shown, a near surface 195 of thecontrol gate 165 is no closer to the substrate than a near surface 191of the floating gate 163, and a far surface 149 of the control gate 165is no farther from the substrate than a far surface 192 of the floatinggate 163. In such a geometry the control gate 124 and the floating gate120 may be thought of as self-aligned, similar to the geometry shown inFIG. 1A.

FIG. 2A shows a side cross-section of an embodiment of a vertical NANDflash string 200 with self-aligned floating gates. A source line 202 maybe formed on top of the base substrate 201. A polysilicon pillar 205 maybe in electrical contact with the source line 202 and extend verticallyfrom the source line 202. The polysilicon pillar 205 may be surroundedby a tunneling dielectric film 212. An insulating layer 203 may separatethe source line 202 from a source select gate 210, which uses a portionof the polysilicon pillar 205 for its channel. The source select gate210 may be separated from the memory cells 250 by insulating layer 204.The base substrate 201, the source line 202, the insulating layer 203,the source select gate 210 and the insulating layer 204, may be thoughtof as the substrate that polysilicon pillar 205, or memory cell body,extends from, and that the NAND string is built around. Otherembodiments may have a different composition of the substrate.

The memory cells 250 may include two or more memory cells 220, 230individually interposed between tier insulating layers 251, 255, 259.The polysilicon pillar 205 is shared by the two or more memory cells220, 230 and extends through the tier insulating layers 251, 255, 259.The first memory cell 220 may include a body formed from a portion ofthe polysilicon pillar 205, and an annular shaped floating gate 222,positioned around the polysilicon pillar 205, and separated from thepolysilicon pillar 205 by a tunneling dielectric film 212. The firstmemory cell 220 may also include a control gate 253, which may surroundthe floating gate 222, and is separated from the floating gate 222 by ablocking dielectric film 221. The floating gate 222 is at least as thickas the control gate 253. The first memory cell 220 may be separated fromthe second memory cell 230 by the tier insulating layer 255. The secondmemory cell 230 may include a body formed from another portion of thepolysilicon pillar 205, and an annular shaped floating gate 232,positioned around the polysilicon pillar 205, and separated from thepolysilicon pillar 205 by a tunneling dielectric film 212. The secondmemory cell 230 may also include a control gate 257, which may surroundthe floating gate 232 and is separated from the floating gate 232 by theblocking dielectric film 231. The floating gate 232 is at least as thickas the control gate 257.

In the embodiment shown in FIG. 2A, sacrificial layers 252, 254 sandwichthe control gate 253, with the sacrificial layer 252 situated betweenthe control gate 253 and the tier insulating layer 251, and thesacrificial layer 254 situated between the control gate 253 and the tierinsulating layer 255. Sacrificial layers 256, 258 sandwich the controlgate 257, with the sacrificial layer 256 situated between the controlgate 257 and the tier insulating layer 255, and the sacrificial layer258 situated between the control gate 257 and the tier insulating layer259. The sacrificial layers 252, 254, 256, 258 are differentiated fromthe tier insulating layers 251, 255, 259 to allow selective etching ofthe sacrificial layers 252, 254, 256, 258 without significantlyimpacting the tier insulating layers 251, 255, 259.

The floating gates 222, 232 are separated from the tier insulatinglayers 251, 255, 259 by blocking dielectric films 221, 231. The blockingdielectric films 221, 231 wrap around the floating gates 222, 232 tocover the top, bottom, and outside of the annulus. The sacrificiallayers 252, 254, 256, 258 are individually no thinner than the blockingdielectric films 221, 231 which keeps the floating gates 222, 232 atleast as thick as the control gates 253, 257. By keeping the sacrificiallayers at least as thick as the blocking dielectric films 221, 231, theshortest path from anywhere in a control gate 253, 257 to thepolysilicon pillar 205, passes through a floating gate 222, 232.

A drain select gate 240 may be separated from the memory cells 250 by aninsulating layer 206 and may couple the body of the NAND string,polysilicon pillar 205, to a bit line 209 through a via 208. The bitline 209 may be separated from the drain select gate 240 by aninsulating layer 207.

FIG. 2B shows a schematic 290 of the NAND flash string 200 of FIG. 2A.The NAND string 200 includes two floating gate field effect transistors(FG-FET) 292, 293 coupled together serially. FG-FET 292 corresponds tothe memory cell 220 and FG-FET 293 corresponds to the memory cell 230.The FG-FET 292 is coupled to field-effect transistor (FET) 291, whichcorresponds to the source select gate 210, with the conductor 298corresponding to the source line 202. FG-FET 293 is coupled to FET 294which corresponds to the drain select gate 240 and conductor 299corresponds to bit line 209.

FIG. 3 is a block diagram of an embodiment of an electronic system 300with memory 310 using three dimensional NAND flash memory withself-aligned floating gates. Supervisory circuitry 301 is coupled to thememory device 310 with control/address lines 303 and data lines 304. Insome embodiments, data and control may utilize the same lines. Thesupervisory circuitry 301 may include a processor, microprocessor,microcontroller, finite state machine, or some other type of controllingcircuitry. The supervisory circuitry 301 may execute instructions of aprogram in some embodiments. In some embodiments, the supervisorycircuitry 301 may be integrated in the same package or even on the samedie as the memory device 310. In some embodiments, the supervisorycircuitry 301 may be integrated with the control circuitry 311, allowingsome of the same circuitry to be used for both functions. Thesupervisory circuitry 301 may have external memory, such as randomaccess memory (RAM) and read only memory (ROM), used for program storageand intermediate data or it may have internal RAM or ROM. In someembodiments, the supervisory circuitry 301 may use the memory device 310for program or data storage. A program running on the supervisorycircuitry 301 may implement many different functions including, but notlimited to, an operating system, a file system, memory block remapping,and error management.

In some embodiments an external connection 302 is provided. The externalconnection 302 is coupled to input/output (I/O) circuitry 305 which maythen be coupled to the supervisory circuitry 301 and allows thesupervisory circuitry 301 to communicate to external devices. In someembodiments, the I/O circuitry 305 may be integrated with thesupervisory circuitry 301 so that the external connection 302 isdirectly coupled to the supervisory circuitry 301. If the electronicsystem 300 is a storage system, the external connection 302 may be usedto provide an external device with non-volatile storage. The electronicsystem 300 may be a solid-state drive (SSD), a USB thumb drive, a securedigital card (SD Card), or any other type of storage system. Theexternal connection 302 may be used to connect to a computer or otherintelligent device such as a cell phone or digital camera using astandard or proprietary communication protocol. Examples of computercommunication protocols that the external connection 302 may becompatible with include, but are not limited to, any version of thefollowing protocols: Universal Serial Bus (USB), Serial AdvancedTechnology Attachment (SATA), Small Computer System Interconnect (SCSI),Fibre Channel, Parallel Advanced Technology Attachment (PATA),Integrated Drive Electronics (IDE), Ethernet, IEEE-1394, Secure DigitalCard interface (SD Card), Compact Flash interface, Memory Stickinterface, Peripheral Component Interconnect (PCI) or PCI Express(PCI-e).

If the electronic system 300 is a computing system, such as a mobiletelephone, a tablet, a notebook computer, a set-top box, or some othertype of computing system, the external connection 302 may be a networkconnection such as, but not limited to, any version of the followingprotocols: Institute of Electrical and Electronic Engineers (IEEE)802.3, IEEE 802.11, Data Over Cable Service Interface Specification(DOCSIS), digital television standards such as Digital VideoBroadcasting (DVB)—Terrestrial, DVB-Cable, and Advanced TelevisionCommittee Standard (ATSC), and mobile telephone communication protocolssuch as Global System for Mobile Communication (GSM), protocols based oncode division multiple access (CDMA) such as CDMA2000, and Long TermEvolution (LTE).

The memory device 310 may include an array 317 of memory cells. Thememory cells may be organized into three dimensional stacks of memorycells, such as vertical NAND strings. The vertical NAND strings mayinclude self-aligned floating gates as discussed above. Address linesand control lines 303 may be received and decoded by control circuitry311, I/O circuitry 313 and address circuitry 312 which may providecontrol to the memory array 317 through the word line drivers 314 andbit line drivers 315. I/O circuitry 313 may couple to the data lines 304allowing data to be received from and sent to the processor 301. Dataread from the memory array 317 may be determined by the sense amplifiers316 and temporarily stored in read buffers 319. Data to be written tothe memory array 317 may be temporarily stored in write buffers 318before being transferred to the memory array 317.

The system illustrated in FIG. 3 has been simplified to facilitate abasic understanding of the features of the system. Many differentembodiments are possible including using a single supervisory circuitry301 to control several memory devices 310 to provide for more storagespace. Additional functions, such as a video graphics controller drivinga display, and other devices for human oriented I/O may be included insome embodiments.

FIG. 4 is a flowchart 400 of an embodiment of a method to fabricate athree dimensional memory structure with self-aligned floating gates, andFIG. 5A-L show cross-sectional side views of various stages of themethod shown in FIG. 4. FIG. 4 and FIG. 5A-L are discussed togetherbelow.

Flowchart 400 may begin to form a 3D memory structure at block 401 andmay create a stackup 500 of at least two alternating tier insulatinglayers and circuit layers above a substrate at block 402, where the wordstackup refers to the layers that may be used to create memory cells.The substrate may include a base wafer or other structure upon whichvarious materials be deposited, grown, or otherwise put in place invarious patterns, layers, and thicknesses with a variety of processes tocreate circuitry for the memory. The substrate may include some numberof layers of other materials on the wafer before the stackup is created.In the embodiment shown in FIG. 5A, a first tier insulating layer 501,second tier insulating layer 505 and third tier insulating layer 509have circuit layers interposed between them with the first circuit layerincluding conductive layer 503 sandwiched between sacrificial layers502, 504 and the second circuit layer including conductive layer 507sandwiched between sacrificial layers 506, 508. Some embodiments mayinclude additional layers, films, or other material, between the variouslayers of the stackup described here. Creating a layer may be performedby any process, including, but not limited to, deposition of a material,implantation or doping of an existing material, or inducing a chemicalreaction at the surface of an existing material. Patterning and/oretching processes may be performed at various stages during theformation of the stackup 500, such as to create individual traces in theconductive layers 503, 507. The materials used may vary betweenembodiments, but in at least one embodiment, the conductive layers 503,507 may be formed using polysilicon, which may be doped to improveconductivity in some embodiments, and the tier insulating layers 501,505, 509 and sacrificial layers 502, 504, 506, 508 may formed using anoxide or nitride, such as silicon oxide or silicon nitride, althoughother materials may be used in other embodiments.

While the tier insulating layers 501, 505, 509 and sacrificial layers502, 504, 506, 508 may be made with different materials in someembodiments, other embodiments may use the same material for the tierinsulating layers 501, 505, 509 and sacrificial layers 502, 504, 506,508. In either case, the tier insulating layers 501, 505, 509 andsacrificial layers 502, 504, 506, 508 are differentiated to allowselective etching of the sacrificial layers 502, 504, 506, 508 withoutetching the tier insulating layers 501, 505, 509. In some embodiments,the sacrificial layers 502, 504, 506, 508 may be modified duringdeposition, using techniques such as, but not limited to, changing thedeposition precursor, the film power, the pressure, or the doping, todifferentiate the sacrificial layers 502, 504, 506, 508 from the tierinsulating layers 501, 505, 509. In other embodiments, the sacrificiallayers 502, 504, 506, 508 may be modified after deposition, usingtechniques such as, but not limited to, plasma processing, thermalannealing, doping, or implantation, to differentiate the sacrificiallayers 502, 504, 506, 508 from the tier insulating layers 501, 505, 509.Any technique and/or material may be used to increase the etch rate ofthe sacrificial layers 502, 504, 506, 508 relative to the tierinsulating layers 501, 505, 509.

At block 403, a hole 520 may be created through the stackup 500, asshown in FIG. 5B. The hole 520 may be created using any process,including, but not limited to chemical and/or mechanical processes. Thehole 520 may be roughly circular in many embodiments, although someembodiments may use other shapes. The conductive layers 503, 507 may beetched back from the hole 520 at block 404 to create cavities 521, 522extending away from the hole 520 as shown in FIG. 5C. The cavities 521,522 may be roughly annular in shape in some embodiments. The sacrificiallayers 502, 504, 506, 508 may be etched back from the hole 520 at block405 as shown in FIG. 5D. In some embodiments the edges 523 of thesacrificial layers 502, 504, 506, 508 are etched back to about the samedistance from the hole 510 as the conductive layers 503, 507, althoughvarious embodiments may target more or less etching of the sacrificiallayers 502, 504, 506, 508 than the conductive layers 503, 507. Theetching processes used in blocks 404 and 405 may be selective toindividually etch the conductive layers 503, 507 and sacrificial layers502, 504, 506, 508 individually, but some embodiments may combine theetching of the conductive layers 503, 507 and sacrificial layers 502,504, 506, 508, to form cavities 521, 522. The etching done in blocks 404and 405 may not etch significant amounts of the tier insulating layers501, 505, 509.

At block 406, the blocking dielectric film may be formed. The blockingdielectric film may be as thick as, or may be thinner than, thesacrificial layers 502, 504, 506, 508 on the tier insulating layers 501,505, 509 inside the cavities 521, 522. Alternatively, in someembodiments, techniques may be used so that no blocking dielectric filmis deposited on the surfaces of the tier insulating layers 501, 505, 509inside the cavities 521, 522. In yet other embodiments techniques may beemployed to remove the blocking dielectric film from the surfaces of thetier insulating layers 501, 505, 509 inside the cavities 521, 522.Depending on the embodiment, the blocking dielectric film may be formedin several steps and may include depositing a blocking dielectric filminside the hole 520, including the cavities 521, 522. In otherembodiments, such as shown in FIG. 5E-5G, the blocking dielectric filmmay include multiple layers that are formed individually. In at leastone embodiment, an outer oxide film 511, 512 is created on an exposedarea of the conductive layers 503, 507 after the etching of theconductive layers 503, 507 as shown in FIG. 5E. The outer oxide film511, 512 may be grown, deposited, or otherwise formed by variouswell-known processes, according to the embodiment. FIG. 5F shows a highdielectric film 513 deposited in the hole 520, including the cavities521, 522 and FIG. 5G shows an inner oxide film 514 deposited on top ofthe high dielectric film 513. The high dielectric film 513 has a higherdielectric constant than the outer oxide film 511, 512 and the inneroxide film 514. The outer oxide film 511, 512 and the inner oxide film514 may be made from silicon oxide in some embodiments, and the highdielectric film 513 may be made from materials such as, but not limitedto, silicon nitride, aluminum oxide, hafnium oxide, or hafnium silicate.

At block 407, material, which may be polysilicon in some embodiments,may be deposited, grown, or otherwise placed to create the floatinggates 515, 516 in the cavities 521, 522 created by the etching of theconductive layers 503, 507 and the sacrificial layers 502, 504, 506, 508as shown in FIG. 5H. The floating gates 515, 516 are separated from theconductive layers 503, 507 and the tier insulating layers 501, 505, 509by the blocking dielectric film, which may include the high dielectricfilm 513 and the inner oxide film 514. Together, the high dielectricfilm 513 sandwiched between the outer oxide film 511, 512 and the inneroxide film 514 may form an oxide-nitride-oxide (ONO) inter-polydielectric (IPD) that may separate control gates formed in theconductive layers 503, 507 from the floating gates 515, 516 of floatinggate memory cells.

In some embodiments, the blocking dielectric film 513, 514 may beremoved from the inside of the hole 525, along with some of the floatinggate material 515, 516 as shown in FIG. 5J (5I is not used to identify afigure to avoid confusion), to provide a smoother, more regular surfacebefore forming, in block 408, a tunneling dielectric film 517 bydepositing, growing, or otherwise creating the tunneling dielectric film517 inside the hole as shown in FIG. 5K. The tunneling dielectric film517 may be an oxide in some embodiments, although other embodiments mayuse a different material. At block 409, the hole 525 may be filled withsemiconductor material 518, which may include polysilicon in someembodiments. Note that the use of the word ‘filled’ both here and in theclaims is not meant to imply that the hole 525 is completely filled withthe semiconductor material 518, as some embodiments may include othermaterial and/or may leave space at the top of the hole 525 that isunfilled. Note that the semiconductor material 518 is separated from thefloating gates 515, 516 by the tunneling dielectric film 517. Theflowchart 400 may then finish at block 410 and the rest of the memorymay be manufactured with additional processes.

By using the method described in FIGS. 4 and 5A-5L, the control gates ofthe memory cells are no thicker than the floating gates and areself-aligned so that a near surface of the control gate is no closer tothe substrate than a near surface of the floating gate, and a farsurface of the control gate is no farther from the substrate than a farsurface of the floating gate. A self-aligned floating gate may bedefined as a floating gate in a structure where a shortest path from anypoint in an associated control gate, to the semiconductor material thatthe fills the hole, passes through the floating gate. Such aself-aligned geometry may reduce tunneling current between the controlgate and the channel of the memory cell and may increase the reliabilityof the floating gate flash memory cell.

Other methods may also be used to form the memory cell with aself-aligned floating gate. In an alternate embodiment of a method tomanufacture a memory, the stackup may be formed without sacrificiallayers, a hole created and the conductive layers etched back from thehole to form annular cavities. An outer oxide film may be grown on theexposed areas of the conductive layers and a nitride film depositedinside of the hole and cavities. Another material that is differentiatedfrom the nitride film may then be deposited in the cavity, such aspolysilicon. The nitride film may then be etched back between the tierinsulating layer and the polysilicon so that only the nitride filmcovering the outer oxide film is left. The polysilicon may then beetched away to expose the nitride film and an inner oxide film that isdifferentiated from the tier insulating layer may then be deposited onthe inside of the hole and cavity. The cavity may then be re-filled withmaterial, such as polysilicon, and then the inner oxide film etched awayuntil only the film in contact with the nitride layer is left, creatingthe oxide-nitride-oxide (ONO) inter-poly dielectric (IPD) layer toseparate the control gate from the floating gate of the memory cell. Thegap between the polysilicon and the tier insulating layer may then befilled with polysilicon to complete the floating gate, or the existingpolysilicon may be etched away and the cavity re-filled with materialfor the floating gate. A tunneling dielectric film may then be depositedinside the hole and the hole filled with semi-conducting material.

The flowchart and/or block diagrams in the figures help to illustratethe architecture, functionality, and operation of possibleimplementations of systems, and methods of various embodiments. Itshould also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved.

Examples of various embodiments are described in the followingparagraphs:

An example memory device may include a memory cell body extending from asubstrate, a self-aligned floating gate separated from the memory cellbody by a tunneling dielectric film, and a control gate separated fromthe floating gate by a blocking dielectric film. In the example memorythe self-aligned floating gate is flanked by the memory cell body andthe control gate to form a memory cell, and the self-aligned floatinggate is at least as thick as the control gate. Some example memorydevices may include sacrificial layers sandwiching the control gate. Insome example memory devices a near surface of the control gate is nocloser to the substrate than a near surface of the self-aligned floatinggate, and a far surface of the control gate is no farther from thesubstrate than a far surface of the self-aligned floating gate. In someexample memory devices the memory cell body, the self-aligned floatinggate and the control gate may be made from polysilicon, the tunnelingdielectric film may be made from of an oxide, and the blockingdielectric film is an inter-poly dielectric comprising a nitride filmsandwiched between two oxide films. In some example memory devices thememory cell body includes a pillar with a substantially circularcross-section, the self-aligned floating gate includes an annulus aroundthe memory cell body, and the control gate surrounds the self-alignedfloating gate. In some example memory devices the self-aligned floatinggate is a first floating gate, the control gate is a first control gate,and the memory cell is a first memory cell. The example memory devicemay also include a second floating gate separated from the memory cellbody by the tunneling dielectric film, a second control gate separatedfrom the second floating gate by the blocking dielectric film, and atier insulating layer. In some example memory devices the first floatinggate and the first control gate are positioned between the substrate andthe tier insulating layer, the second floating gate and the secondcontrol gate are positioned on an opposite side of the tier insulatinglayer from the first floating gate and the first control gate, and thememory cell body extends through the tier insulating layer. In someexample memory devices the second floating gate is flanked by the memorycell body and the second control gate to form a second memory cell, andthe second floating gate is at least as thick as the second controlgate. Some example memory devices may also include a first sacrificiallayer situated between the first control gate and the tier insulatinglayer, and a second sacrificial layer situated between the tierinsulating layer and the second control gate. In some example memorydevices, the first and second sacrificial layers are differentiated fromthe tier insulating layer. In some example memory devices the first andsecond floating gates are separated from the tier insulating layer bythe blocking dielectric film, and the first and second sacrificiallayers are individually no thinner than the blocking dielectric film.Any combination of the examples of this paragraph may be used inembodiments.

An example electronic system may include supervisory circuitry, and atleast one memory device coupled to the supervisory circuitry. The memorydevice in the example electronic system may be any of the example memorydevices described in the previous paragraph. The memory device in theexample electronic system may include two or more memory cellsindividually interposed between tier insulating layers. A memory cell ofthe two or more memory cells may include a body formed in a portion of apolysilicon pillar, an annular shaped floating gate positioned aroundthe polysilicon pillar, and separated from the polysilicon pillar by atunneling dielectric film, and a control gate that surrounds thefloating gate and is separated from the floating gate by a blockingdielectric film. In the memory cell in some example electronic systemsthe floating gate is at least as thick as the control gate, and thepolysilicon pillar is shared by the two or more memory cells and extendsthrough the tier insulating layers. Some example electronic systems mayalso include I/O circuitry coupled to the supervisory circuitry. Someexample electronic systems may be a solid-state drive. In a memory cellof some example electronic systems a shortest path from any point in thecontrol gate to the polysilicon passes through the floating gate. Amemory cell of some example electronic systems may also includesacrificial layers situated between the control gate and the tierinsulating layers. In a memory cell of some example electronic systemsthe sacrificial layers are differentiated from the tier insulatinglayers. In a memory cell of some example electronic systems the floatinggate is separated from the tier insulating layers by the blockingdielectric film, and the sacrificial layers are individually no thinnerthan the blocking dielectric film. In a memory cell of some exampleelectronic systems the floating gate and the control gate are formedfrom polysilicon, the tunneling dielectric film is made with an oxide,and the blocking dielectric film is an inter-poly dielectric including anitride film sandwiched between two oxide films. Any combination of theexamples of this paragraph may be used in embodiments.

An example method of manufacturing a memory device may include creatinga stackup of at least two alternating tier insulating layers and circuitlayers individually including a conductive layer sandwiched betweensacrificial layers that are differentiated from the tier insulatinglayer, creating a hole through the stackup, etching the conductivelayers back from the hole, etching the sacrificial layers back from thehole, forming a blocking dielectric film no thicker than an individualsacrificial layer of the sacrificial layers inside the hole, creatingfloating gates in the cavities created by the etching of the conductivelayers and the sacrificial layers so that the floating gates areseparated from the conductive layers and the tier insulating layers bythe blocking dielectric film, forming a tunneling dielectric film insidethe hole, and filling the hole with semiconductor material, so that thesemiconductor material is separated from the floating gates by thetunneling dielectric film. In some example methods of manufacturing amemory device the conductive layers, the floating gates and thesemiconductor material are made from polysilicon, and the tierinsulating layers and the sacrificial layers are made from an oxide or anitride. Some example methods of manufacturing a memory device may alsoinclude creating an outer oxide film on an exposed area of theconductive layers after the etching of the conductive layers so that theblocking dielectric film includes a high dielectric film and an inneroxide film, the high dielectric film having a higher dielectric constantthan the inner and outer oxide films, and the conductive layers areseparated from the floating gates by an inter-poly dielectric comprisingthe high dielectric film sandwiched between the outer oxide film and theinner oxide film. In some example methods of manufacturing a memorydevice the inner and outer oxide film are made from silicon oxide, andthe high dielectric film is made from silicon nitride, aluminum oxide,hafnium oxide, or hafnium silicate. In some example methods ofmanufacturing a memory device creating the stackup includes modifyingthe sacrificial layers during deposition to differentiate thesacrificial layers from the tier insulating layers. In some examplemethods of manufacturing a memory device the creating the stackup mayinclude treating the sacrificial layers after deposition todifferentiate the sacrificial layers from the tier insulating layers.Any combination of the examples of this paragraph may be used inembodiments.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. Furthermore, as used in this specificationand the appended claims, the term “or” is generally employed in itssense including “and/or” unless the content clearly dictates otherwise.As used herein, the term “coupled” includes direct and indirectconnections. Moreover, where first and second devices are coupled,intervening devices including active devices may be located therebetween.

The description of the various embodiments provided above isillustrative in nature and is not intended to limit this disclosure, itsapplication, or uses. Thus, different variations beyond those describedherein are intended to be within the scope of embodiments. Suchvariations are not to be regarded as a departure from the intended scopeof this disclosure. As such, the breadth and scope of the presentdisclosure should not be limited by the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and equivalents thereof.

What is claimed is:
 1. A memory device comprising: a memory cell bodyextending from a substrate; a self-aligned floating gate separated fromthe memory cell body by a tunneling dielectric film; a control gateseparated from the floating gate by a blocking dielectric film; whereinthe self-aligned floating gate is flanked by the memory cell body andthe control gate to form a memory cell, and the self-aligned floatinggate is at least as thick as the control gate; wherein the memory cellbody comprises a pillar with a substantially circular cross-section, theself-aligned floating gate comprises an annulus around the memory cellbody, and the control gate surrounds the self-aligned floating gate; andwherein the floating gate and the control gate are positioned betweenthe substrate and a tier insulating layer, and the pillar with asubstantially circular cross-section extends through the tier insulatinglayer.
 2. The memory device of claim 1, further comprising sacrificiallayers sandwiching the control gate.
 3. The memory device of claim 1,wherein a near surface of the control gate is no closer to the substratethan a near surface of the self-aligned floating gate; and a far surfaceof the control gate is no farther from the substrate than a far surfaceof the self-aligned floating gate.
 4. The memory device of claim 1,wherein the memory cell body, the self-aligned floating gate and thecontrol gate comprise polysilicon; the tunneling dielectric film iscomprised of an oxide; and the blocking dielectric film is an inter-polydielectric comprising a nitride film sandwiched between two oxide films.5. The memory device of claim 1, wherein the self-aligned floating gateis a first floating gate, the control gate is a first control gate, andthe memory cell is a first memory cell, the memory device furthercomprising: a second floating gate separated from the memory cell bodyby the tunneling dielectric film; a second control gate separated fromthe second floating gate by the blocking dielectric film; and the tierinsulating layer; wherein the second floating gate and the secondcontrol gate are positioned on an opposite side of the tier insulatinglayer from the first floating gate and the first control gate; andwherein the second floating gate is flanked by the memory cell body andthe second control gate to form a second memory cell, and the secondfloating gate is at least as thick as the second control gate.
 6. Thememory device of claim 5, further comprising: a first sacrificial layersituated between the first control gate and the tier insulating layer;and a second sacrificial layer situated between the tier insulatinglayer and the second control gate; wherein the first and secondsacrificial layers are differentiated from the tier insulating layer. 7.The memory device of claim 6, wherein the first and second floatinggates are separated from the tier insulating layer by the blockingdielectric film; and the first and second sacrificial layers areindividually no thinner than the blocking dielectric film.
 8. Anelectronic system comprising: supervisory circuitry; and at least onememory device coupled to the supervisory circuitry, the memory devicecomprising two or more memory cells individually interposed between tierinsulating layers; a memory cell of the two or more memory cellscomprising: a body comprising a portion of a polysilicon pillar; anannular shaped floating gate positioned around the polysilicon pillar,and separated from the polysilicon pillar by a tunneling dielectricfilm; and a control gate that surrounds the floating gate and isseparated from the floating gate by a blocking dielectric film; whereinthe floating gate is at least as thick as the control gate, and thepolysilicon pillar is shared by the two or more memory cells and extendsthrough the tier insulating layers.
 9. The electronic system of claim 8,further comprising I/O circuitry coupled to the supervisory circuitry.10. The electronic system of claim 8, wherein the electronic systemcomprises a solid-state drive.
 11. The electronic system of claim 8,wherein a shortest path from any point in the control gate to thepolysilicon passes through the floating gate.
 12. The electronic systemof claim 8, the memory cell further comprising sacrificial layerssituated between the control gate and the tier insulating layers;wherein the sacrificial layers are differentiated from the tierinsulating layers.
 13. The electronic system of claim 12, wherein thefloating gate is separated from the tier insulating layers by theblocking dielectric film; wherein the sacrificial layers areindividually no thinner than the blocking dielectric film.
 14. Theelectronic system of claim 13, wherein the floating gate and the controlgate comprise polysilicon; the tunneling dielectric film comprise anoxide; and the blocking dielectric film is an inter-poly dielectriccomprising a nitride film sandwiched between two oxide films.